Can a substance be a lewis acid without being a bronsted-lowry acid? argue

Yes

Explanation:

Yes, A substance can be a lewis acid without being a Bronsted-Lowery acid because there are some substances which cannot donate protons (Bronsted-Lowery acid) but can accept a pair of electron.

For Example:

Let us take the example of BF₃

BF₃ contains no proton so it is not a Bronsted Lowery Acid

However, BF₃ has an incomplete octet with 6 electrons. It needs an electron pair to complete its octet. It accepts a pair of electron to become a Lewis Acid

Interesting question, and the answer is yes, a substance can be a Lewis acid but not a Bronsted-Lowrey acid. To see this, let's take a look at the definitions of each.

Explanation:

Bronsted-Lowrey acid:

A compound that is a hydrogen ion (proton) donor. When dissolved in the solvent in question, these compounds lose a proton to the solution. The concentration of these protons in solution is referred to as acidity, and is measured on the pH scale.

Lewis acid:

A substance that is an electron pair receiver. In solution, free electron pairs will form bonds with the substance, either ionic or covalent. In this definition, a proton is itself an acid, rather than a part of an acid.

A key thing to note here is that, in the Bronsted-Lowrey definition, there must be a proton. That means, all Bronsted-Lowrey acids are of the form HXn→H++Xn-, showing the dissociation in solution. However, a Lewis acid needs only to have the ability to accept an electron pair, which means that H + is a Lewis acid, instead of what makes a compound an acid. Additionally, that means that the number of compounds that qualify as a Lewis acid are expanded. A favorite example of mine is boron trifluoride, or BF3. It is a common reagent in organic synthesis, it is a Lewis acid, but does not have any hydrogen, so it cannot be a Bronsted-Lowrey acid